INTRODUCTION On 22 March 2003, the Ministry of Health, Singapore, designated Tan Tock Seng Hospital as the nationwide severe acute respiratory syndrome (SARS) hospital and its Emergency Department (ED) took over the role as the screening center for SARS on 26 March 2003. We describe the initial clinical characteristics of probable or suspect SARS patients that presented to the ED. METHODS A retrospective study of patients who were admitted through the ED and subsequently diagnosed to have probable SARS and suspect SARS was done. The data of these patients from the ED log were reviewed and analysed. RESULTS From 13 March 2003 to 31 May 2003, 11,461 patients were screened for SARS and 1,386 patients were admitted. Of these, 117 patients were diagnosed to have probable SARS and 146 suspect SARS. Their mean age was 36.7 years (range 1-80). Among these patients, there were 122 men (46.4 percent), and 205 were Singaporeans (77.9 percent). 13 patients had no initial contact history upon presentation to the ED. The mean duration between onset of symptom to presentation to the ED was 3.1 days. Travel history was less common in probable SARS cases than in suspect SARS cases as the epidemic was due mainly to local transmission. Fever was the most common presenting symptom (91.6 percent), and gastrointestinal symptoms were the least (6.9 percent). In the ED, 249 (94.7 percent) patients had chest radiographs and 86 (32.7 percent) had full blood count done. 22.2 percent of probable SARS patients had normal chest radiographs when they first presented to the ED. CONCLUSION The World Health Organisation criteria were important screening tools and admission guides, but should not be strictly followed. It was difficult to differentiate between probable and suspect SARS patients in the ED.